The Q&A Archives: Lawn - St. Augustine problems

Question: I sodded with St. Augustine and the center of my lawn is barely growing. The results of my soil test were that I have sandy clay. The ph is 6.5. It is low in organic material. It is also low in nitrates, phosphorus, potassium and calcium. It sounds to me that my lawn is anemic. It is high in iron, manganese and zinc. Can you suggest a program for me to get my yard back in shape....

Answer: After establishment the success of St. Augustine grass as a lawn grass depends largely on management. Mowing, fertilization and supplemental watering are required to maintain a dense, green, weed-free turf of St. Augustine grass. In coastal areas where rainfall is adequate, St. Augustine grass will survive with little care. In inland areas, where rainfall is less dependable, close management of water is required to maintain a satisfactory lawn with St. Augustine grass.

The growth rate of St. Augustine grass is dependent on temperature, moisture availability and nutrient availability. Any one of these factors can limit the rate of growth of this species. In the spring with mild daytime temperatures and cool night temperatures, St. Augustine grass greens up, but makes little growth. As day and night temperatures increase during late spring and summer, the growth rate increases. Thus, an established turf of St. Augustine grass may require mowing every 2 weeks in early spring and as often as every five days by late spring if nitrogen fertilizer is applied.

During the fall, as temperatures cool, St. Augustine grass maintains its dark green color, but its growth rate declines sharply. Mowing frequency may be reduced to twice monthly during late fall and early winter.

Mowing heights may range from 1 to 3 inches depending on the frequency of mowing and the degree of shade present. At mowing heights below two inches, St. Augustine grass should be mowed every five days during late spring and summer. At a 2 1/2 inch mowing height, a 7-10 mowing schedule is adequate. Above 2 1/2 inches, St. Augustine grass should be mowed at 10 to 14 day intervals. In moderate to dense shade, St. Augustine grass should be mowed at about 3 inches at 10 day intervals.

During the fall, mowing height should be raised about ? inch to increase total leaf area of the turf. The increased leaf area will help the grass accumulate energy reserves to get through the winter. The greater leaf area will also help prevent weed invasion during the dormant season.

St. Augustine grass is responsive to nitrogen fertilizer in terms of color and growth rate. On sandy soils St. Augustine grass requires about 1 pound of nitrogen per 1,000 square feet per month during the growing season to maintain satisfactory color and density. At rates above 1 pound per 1,000 square feet, St. Augustine grass produces lush growth that is highly susceptible to insects and diseases. On heavier textured soils ? pound of nitrogen every month is adequate to maintain good color and growth. Thatch accumulation is also a problem when nitrogen fertilization exceeds the required rate.

Late fall fertilization of St. Augustine grass helps maintain color and density of the lawn into the winter and promotes early recovery of the grass in the spring. Thus, to extend the length of time a St. Augustine lawn is attractive, the lawn should receive about 1 pound of nitrogen every 30 to 60 days from early spring through late fall.

St. Augustine grass is sensitive to iron deficiency and readily develops chlorotic symptoms in alkaline or iron deficient soils. This deficiency can be corrected with foliar applications or iron sulfate or iron chelate. Soil applications of iron sources are less effective than foliar application in alkaline soils.

Potassium requirements for St. Augustine grass are about the same as for other grasses. About half as much potassium as nitrogen is required to maintain growth. Potassium has been shown to increase root growth, cold tolerance and drought tolerance in St. Augustine grass.

Phosphorous requirements for established St. Augustine grass are very low and generally met from the soil. Occasional applications of a phosphorous fertilizer material may be required. Newly planted St. Augustine grass will respond to phosphorous fertilizers in terms of an increased rate of spread.

Best wishes with your lawn!

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